I'm not sure if Cromlix will be making profits yet. I'm sure Andy or someone else involved said something about expecting it to take a few years of investment, which is typical for that sort of business. However, the Times list isn't just about income, it's about assets. So while Andy may have spent a lot of money buying and doing up the building, he's got himself a business, which will have an estimated value, which would account for anticipated profits as well as the value of the property itself.
Andy's worth has got to be quite tough to calculate, because while they might know his official prize money, and might be able to make a stab at what he gets from endorsements, they will also have to guess how much he spends on general tennis expenses like travel, hotels and everyone who works on his team. They can check company accounts, but it's still a lot of guesswork. We'd never have known about him donating his Queen's prize money to the Royal Marsden if big gob Andrew hadn't spilled the beans, and then there's all those flowers for the wedding!
It's notable that the articles I've read have all mentioned Lewis being a tax exile. Presumably he'd have a lot less if he did pay full tax like the rest of them. I've nothing against people making sensible and reasonable tax decisions, but you do wonder how much money anyone needs to want to be a tax exile. Not that I'm bitter or anything, but driving a car isn't a proper sport either!